1. Field of the Invention
This invention relates to a deflection angle detecting device and a system provided with the deflection angle detecting device, and in particular, to a deflection angle detecting device constructed as a tracking detecting means used for light pickup or a light-switching means of an optical fiber used for optical communication and a system provided with this deflection angle detecting device.
2. Description of Related Art
Recently, the techniques of optical information communication and record have been conspicuously developed and the densities of information transfer and record have been significantly improved. In these fields, it is essential to improve the technique that a deflection state of a light-deflecting mirror element, such as an optical signal switch optically switching an optical fiber circuit at a relay station or the tracking control of light pickup of an optical information record reproducing system, is detected with a high degree of accuracy to control its behavior. As such, various deflection angle detecting devices have been proposed.
Deflection angle detecting devices of this type are disclosed, for example, in Japanese Patent Publication No. Hei 7-66554 and Japanese Patent Kokai Nos. Hei 8-227552, Hei 11-144273, Hei 11-144274, and Hei 11-195236.
A deflection angle detecting device set forth in Hei 7-66554 is designed to detect a relative angle made by the optical axis of a light beam emerging toward the recording medium of light pickup with the recording surface of the recording medium. This device includes a light-emitting element for irradiating the recording surface with diffused light and two light-receiving elements arranged on both sides of the light-emitting element to detect reflected light from the recording surface. The device uses a difference between the amounts of reflected light detected by the two light-receiving elements to thereby detect the amount of deflection where deflection is caused to the recording medium.
A deflection angle detecting device disclosed in Hei 8-227552 is similarly designed to detect a relative angle made by the optical axis of a light beam emerging toward the recording medium of light pickup with the recording surface of the recording medium. This device receives reflected light from the recording medium on the light-receiving surface which is divided into four, and uses a difference between the amounts of received light to thereby detect the amounts of defection in two directions.
A deflection angle detecting device set forth in each of Hei 11-144273 and Hei 11-144274 is such that reflected light from a deflecting mirror is passed through a beam splitter in which the reflectance is changed in accordance with an angle of incidence and the amount of light is detected by a photodetector to thereby detect the amount of deflection.
A deflection angle detecting device described in Hei 11-195236 is designed to detect the position of rotation of a deflecting mirror in an optical information reproducing apparatus. A light beam from a laser source is condensed into a linear beam on the deflecting mirror, and thereby measurement accuracy in one direction is improved to detect the deflection angle.